This invention relates generally to flat panel display devices and particularly to a focus mesh structure and biasing technique for such devices.
U.S. Reissue Pat. No. Re. 30,195 to C. H. Anderson et al., discloses a flat panel display device in which a backplate and a faceplate are spaced in parallel planes. A plurality of vanes extend between the backplate and faceplate to divide the envelope into a plurality of channels and to support the faceplate and backplate against atmospheric pressure after the envelope is evacuated. Arranged in each of the channels is a pair of spaced apart parallel beam guide meshes which extend longitudinally along the channels and transversely across the channels. The beam guide meshes serve as guides along which electron beams are propagated the lengths of the channels.
The inside surface of the faceplate is provided with a phosphor screen which luminesces when struck by electrons. A plurality of extraction electrodes are arranged along the backplate and are used to eject the electron beams from between the beam guide meshes to direct the electron beams toward the phosphor screen. Deflection electrodes are provided on the sides of the support vanes and are electrically energized to cause the electrons to transversely scan across the channels. Accordingly, each of the channels contributes a portion of the total visual display of the device.
U.S. Pat. No. 4,137,478 to T. L. Credelle, discloses a flat panel display device of the element scale type which utilizes a separate guide and electron beam for each color element in every line of the visual display. This device therefore does not employ deflection electrodes. The electron beams are directed toward the desired line by appropriately biasing one of many focusing means which extend across the device. The number of focusing wires is at least equal to the number of lines in the display.
The inventions described in the above-referenced patents are quite satisfactory for the purpose intended. For the purpose of their disclosure, U.S. Pat. Nos. Re. 30,195 and 4,137,478 are hereby incorporated by reference. However, a display device intended for use with standard NTSC television signals must be capable of scanning approximately 525 lines. Accordingly, the meshes of the Anderson device must contain a number of rows of apertures which equals at least one half the number of lines in the display. Similarly, the number of wires in the Credelle device must at least equal the number of lines in the display. The dimensions, and accordingly the tolerances in both devices, therefore, are very tight making the devices very difficult to manufacture.
The instant invention overcomes these difficulties by the provision of a focus mesh structure and biasing techniques which permit greatly increased dimensions and substantially relaxed tolerances.